Shelepen's withdrawal and Nagasu's replacement spot were announced on 11/12--11 days before the start of NHK. It's quite likely that the JSF was notified within the 14-day period and chose the replacement before making the announcement.
Czisny announced her withdrawal yesterday, 11/14 (11/15 in Japan). The JSF decided it was too late to replace Czisny.

I believe Osmond mentioned in an interview after SCI that they had a plan for the year and was sticking to it. Osmond doesn't have to compete at Challenge as she has a Bye to Nationals. From what she said, the plan was to do Nebelhorn and SCI and then get back to the regular training leading up to Challenge and Nationals. She mentioned a couple of times the plan was to achieve 170 this year. She has already achieved that twice internationally. She says she wants to maintain that 170. If she does, she will easily win Challenge and Nationals and will do well at 4CC and Worlds. She said in a TV interview the goal this year was to win Nationals and go to Worlds.